This invention generally relates to methods and apparatus for manufacturing plastic zippered bags of the type in which material, such as foodstuff and detergent, are stored.
Reclosable bags are finding ever-growing acceptance as primary packaging, particularly as packaging for foodstuffs such as cereal, fresh vegetables, snacks and the like. Such bags provide the consumer with the ability to readily store, in a closed, if not sealed, package any unused portion of the packaged product even after the package is initially opened.
Reclosable plastic zipper assemblies are useful for sealing thermoplastic pouches or bags. Typically, the plastic zippers include a pair of interlockable profiled members that form a closure. As the slider moves across the closure members, the profiles are opened or closed. The profiles in plastic zippers can take on various configurations, e.g. interlocking rib and groove elements having so-called male and female profiles, interlocking alternating hook-shaped closure elements, etc.
Machinery for continuously manufacturing zippered bags at high speed is well known. A typical pre-made bag system comprises a station for continuously paying out a web of bag making film from a roll; a folding mechanism for folding the film; a station for continuously paying out a zipper tape and inserting the tape between the opposing walls of the folded bag making film in the machine direction; a station for continuously conduction heat sealing the zipper tape to both walls of the bag making film; a station for ultrasonically welding the zipper at regular package width intervals; a station for cross sealing (again using heat conduction) the zipper/film assembly at the same regular package width intervals to form side seals; and a station for cutting the zipper/film assembly along a midline of the zipper crush and the cross seal to sever a bag from the remainder of the film. In a known pre-made bag system, the film moves continuously through the zipper sealing station, but intermittently through the ultrasonic welding, cross sealing and cutting stations. This transition is effectuated by a synchronization section having motor-driven pinch rolls and a dancer that converts continuous motion into start-stop motion.
Known pre-made bag systems of the above-described type can produce bags at a rate of 200 bags per minute. It would be desirable to increase the production rate of such pre-made bag systems. The limiting factor in speed is the time required to perform an ultrasonic crush of the zipper tape. Thus there is a need for an apparatus for ultrasonically welding the zipper that can operate at faster speeds.
The invention is directed to a method and an apparatus for producing zippered bags at faster speeds. This is accomplished by speeding up the ultrasonic welding operation. More specifically, ultrasonic welding is performed continuously while the web of bag making film and the zipper tape are moving, instead of being performed while the film and zipper tape are stopped. To facilitate this improvement, the ultrasonic welding station is moved from the bag machine, where the bag making film and zipper tape move intermittently, to the sealer frame, where the film and zipper tape move continuously.
One aspect of the invention is a method comprising the following steps: continuously moving a thermoplastic zipper tape along a path; and ultrasonically welding the zipper tape at successive spaced zones along its length at a rate of welding while the zipper tape is moving along the path.
Another aspect of the invention is a method comprising the following steps: incrementally inserting a thermoplastic zipper tape between opposing edges of a folded web of thermoplastic bag making film; continuously moving the folded web and the inserted zipper tape together along a path; incrementally sealing the inserted zipper tape to the folded web of bag making film in a lengthwise direction of the zipper tape while the zipper tape and the web of bag making film are moving together, the incremental sealing occurring along a first segment of the path; and ultrasonically welding the zipper tape and adjoining web portions at successive spaced zones while the zipper tape and the web of bag making film are moving together, the ultrasonic welding occurring along a second segment of the path spaced apart from the first segment.
A further aspect of the invention is an apparatus comprising: a welding station comprising first and second rotary elements arranged with mutually parallel axes of rotation, the first and second rotary elements comprising respective peripheries that are in mutual opposition at a gap; a transducer for converting electric potential differences into ultrasound wave energy, the first rotary element being acoustically coupled to the transducer; drive means for causing the first and second rotary elements to rotate in opposite directions; means for continuously moving a thermoplastic zipper tape along a path that passes through the gap between the first and second rotary elements; and means for acoustically coupling acoustic wave energy from the first rotary element into the zipper tape at spaced intervals along the zipper tape.
Another aspect of the invention is an apparatus for continuously sealing a thermoplastic zipper tape inside opposing edges of a folded web of thermoplastic bag making film. The apparatus comprises: a first pair of mutually opposing sealing bars for incrementally sealing the zipper tape to the folded web of bag making film in a lengthwise direction of the zipper tape while the zipper tape and the folded web are moving together; and rotary ultrasonic apparatus for ultrasonically welding the zipper tape and adjoining portions of the folded web at successive spaced zones along the zipper tape at a rate of welding while the sealed zipper tape/web assembly is moving.
Yet another aspect of the invention is an apparatus comprising: means for continuously moving a web of thermoplastic bag making film and a thermoplastic zipper tape together in adjoining relationship; a stationary conduction heat sealer arranged to continuously seal the zipper tape to the web of bag making film while the zipper tape and the web are moving; first and second rotary elements arranged with mutually parallel axes of rotation and with peripheral surfaces separated by a gap through which the zipper tape and adjoining portions of the web pass, the first rotary element comprising a protuberance on its periphery, the protuberance passing through the gap during rotation of the first rotary element; and an ultrasonic transducer for converting electrical energy into ultrasonic wave energy, wherein the ultrasonic transducer is acoustically coupled to one of the first and second rotary elements.
Other aspects of the invention are disclosed and claimed below.